Guide wire and catheter devices are commonly used to deliver medical therapy, such as stents, through the vasculature of the body to a target region. Navigation of a conventional guide wire involves rotating or applying a torque to the proximal end of the guide wire repeatedly to rotate the distal tip while the wire is pushed. This action is repeated until, by trial and error, the tip enters the desired vessel branch. In navigating guide wires in the vasculature of the body, it is desirable that the tip of the guide wire be flexible enough to negotiate the sharp turns that are necessary to reach the target area for delivery of medical therapy. However, after the guide wire has made several bends, it becomes increasingly difficult to control, often requiring repeated attempts to enter or gain access to a desired vessel branch. This trial and error method can frustrate the physician and cause additional wall contact and potential trauma to the vessel.
In addition, once a guide wire has been positioned within the subject's body, it is necessary to deliver a therapeutic device for procedures such as balloon angioplasty, atherectomy, or coronary stents. Often, a guide wire can be guided to the target site but it becomes difficult or impossible to guide a therapeutic device to the same location. This failure commonly results from the inability of stiffer balloon catheters and stent delivery systems to conform to the bends and turns of the vasculature. This problem has become very relevant due to the increased success, in recent years, of guide wire navigation to remote locations via tortuous paths.
To address some of these difficulties, magnetically navigable guide wires and balloon catheters have been developed which can be controlled with the application of an external magnetic field. An example of a magnetically navigable tether wire is disclosed in Werp et al., U.S. Pat. No. 5,931,818 (incorporated in its entirety herein by reference) and a magnetically navigable guide wire is disclosed in U.S. patent application Ser. No. 10/337,236, filed Jan. 6, 2003, for Magnetically Navigable Medical Guidewire. When the distal end of the guide wire is proximal to the branch of interest, the user operates a magnetic system to apply a magnetic field (with the aid of a computerized user interface) to deflect the wire tip into the vessel branch. This magnet system can frequently direct the distal end of the guide wire into a vessel on a first effort, eliminating the trial and error of manually operated guide wires and thereby reducing or eliminating trauma to the vessel wall. While existing magnetic guidewires are much easier to navigate than conventional guide wires, when carrying a stent the added stiffness can make navigation more difficult.